A Fold s a is a generalization of something Foldable. It allows
you to extract multiple results from a container. A Foldable container
can be characterized by the behavior of
foldMap :: (Foldable t, Monoid m) => (a -> m) -> t a -> m.
Since we want to be able to work with monomorphic containers, we could
generalize this signature to forall m. Monoid m => (a -> m) -> s -> m,
and then decorate it with Const to obtain

Note: When applied to a Traversal, takingWhile yields something that can be used as if it were a Traversal, but
which is not a Traversal per the laws, unless you are careful to ensure that you do not invalidate the predicate when
writing back through it.

Note: Many uses of this combinator will yield something that meets the types, but not the laws of a valid
Traversal or IndexedTraversal. The Traversal and IndexedTraversal laws are only satisfied if the
new values you assign also pass the predicate! Otherwise subsequent traversals will visit fewer elements
and Traversal fusion is not sound.

Note: This function type-checks as a Traversal but it doesn't satisfy the laws. It's only valid to use it
when you don't insert any whitespace characters while traversing, and if your original String contains only
isolated space characters (and no other characters that count as space, such as non-breaking spaces).

Note: This function type-checks as a Traversal but it doesn't satisfy the laws. It's only valid to use it
when you don't insert any newline characters while traversing, and if your original String contains only
isolated newline characters.

The findOf function takes a Lens (or Getter, Iso, Fold, or Traversal),
a predicate and a structure and returns the leftmost element of the structure
matching the predicate, or Nothing if there is no such element.

The findMOf function takes a Lens (or Getter, Iso, Fold, or Traversal),
a monadic predicate and a structure and returns in the monad the leftmost element of the structure
matching the predicate, or Nothing if there is no such element.

The ifindOf function takes an IndexedFold or IndexedTraversal, a predicate that is also
supplied the index, a structure and returns the left-most element of the structure
matching the predicate, or Nothing if there is no such element.

When you don't need access to the index then findOf is more flexible in what it accepts.

The ifindMOf function takes an IndexedFold or IndexedTraversal, a monadic predicate that is also
supplied the index, a structure and returns in the monad the left-most element of the structure
matching the predicate, or Nothing if there is no such element.

When you don't need access to the index then findMOf is more flexible in what it accepts.